Analysis of Cogging Torque Reduction Techniques in Axial-Field Flux-Switching Permanent-Magnet Machine

An axial-field flux-switching permanent-magnet machine (AFFSPMM) is suitable to be used in wind power generation and electric vehicles. However, the cogging torque (Tcog) is large. To obtain high-performance AFFSPMM, the reduction of Tcog in AFFSPMM is investigated. The theoretical Tcog expression is deduced. Based on a 3-D finite-element method, the influences of the design parameters on the Tcog and the reduction methods of Tcog, such as rotor tooth skewing (RTS), rotor tooth circumferential pairing (RTCP), and rotor tooth notching (RTN), are analyzed. The design parameters, except the axial length of rotor, have influences on Tcog, and optimizing the design parameters can decrease Tcog. Tcog can be greatly reduced by RTS for AFFSPMM with a parallel stator tooth and fan-shape permanent-magnet structure. However, RTS is not effective in reducing Tcog for AFFSPMM with a fan-shape stator tooth and parallel PM (FSST-PPM) structure. Tcog greatly decreases by RTN and RTCP for an FSST-PPM stator structure. Moreover, the reduction effect of Tcog with RTN is better than that with RTCP.